It is known to provide an electroluminescent element, arranged for example in the form of a lighting unit or a display, especially as a flat panel display. Flat panel displays are described in “Display interfaces”, R. L. Myers, Wiley, 2002. The electroluminescent element of a flat panel display may comprise one or more devices such as light emitting diodes (LED's), organic light emitting diodes (OLED), Liquid Crystals elements (LCD), Plasma elements (PDP), electroluminescent inorganic elements (EL-Displays), Field Emission elements (FED). If only one such device is used, or a small number of them, dissipation of heat generated during emission of light does not generally pose any great problem. Many devices of this type do not, however, produce much light individually and need to be grouped into arrays in order to be useful for many applications. The collective heat generated by such arrays may prove harmful to the devices forming the array and the ability to dissipate it will dictate the density of devices in the array and their durability. This problem is particularly acute in tiled display apparatus, which may be assembled by juxtaposition of a plurality of arrays and provide little scope for peripheral heat dissipation due to their abutting each other along their side edges. Further, electroluminescent materials used may degrade at different rates at different temperatures. For example, aging may result in lower luminosity and/or colour shifts and therefore to variations in display quality across a large display area. Where displays have to be sealed against water or dust this sealing can increase the difficulty of extracting heat.
In U.S. Pat. No. 6,161,910 an LED reading light is proposed in which an array of white LED's are provided with a tubular housing including two heat sinks. One heat sink is to the rear of the device behind an LED drive circuit and a front heat sink is interposed between the LED array and the drive circuit. The front heat sink is connected, via a thermal pad, to the rear side of the LED array. Heat generated by the LED's is transferred by conduction to the front heat sink, from where it flows radially outward to the tubular housing and then rearward to the rear heat sink. Such an arrangement concentrates heat dissipation around a periphery of the array. This makes it less than ideal for use in a tiled array, where adjoining tiles would all be dissipating heat around their abutting edges. In addition, it will be noted that at least a portion of the heat generated by the LED's must be transported from the LED heat sink to a further (i.e. rear) heat sink before being dissipated. Thus temperature gradients are probably inevitable except at low power. Also the display has a considerable thickness or depth and weight caused by the plurality of heat sinks which need to contain significant amounts of metal to be effective.
In U.S. Pat. No. 6,255,786 an LED display is disclosed for signs and proposes passive and active heat dissipation. Passive dissipation is proposed in the form of conduction from connector legs of the LED's to a solder pad of a circuit board. The whole circuit board is in turn connected to a rear-mounted heat sink via a heat pad. As the density of LED's increases, an active heat transfer device may be introduced in the form of a fan blowing onto the heat sink. Like the lamp of U.S. Pat. No. 6,161,910, at least a portion of the heat generated by the LED's in this proposal must be transported from one heat sink (the solder pad) to a further (rear) heat sink for dissipation. Thus temperature gradients will be caused. An arrangement such as the one proposed in U.S. Pat. No. 6,255,786 may prove bulky for use in a tiled array, requiring a rear mounted fan for each tile. Cooling air being blown onto the rear of the heat sink may be deflected sideways off the heat sink and interfere with the equivalent arrangement of adjacent arrays.
It is known to tile flat panel displays. Two types of tiled displays are shown schematically in FIGS. 11a and B. In FIG. 11a two tiles 90, 91 are shown of the type where connections 94–96 to the light emitting elements of the arrays are attached to the side of the panels. LCD tiled displays can be made in this manner as described in US Patent Application 2002/0080302. The side connections require a T connector 96 between the tiles in one direction which should preferably be as narrow as possible. In the other direction T-connectors 94, 95 are provided. A mask 93 obscures the unsightly connection between the two tiles 90, 91. The connectors 94,96 extend in a direction opposite to the display direction.
In FIG. 11b two tiles 97, 98 are shown of the type where connections 99,100 connected to the light emitting elements of the arrays are attached to the rear side of the panels 97, 98. LED tiled displays can be made in this manner, for example as supplied by BARCO N.V. Belgium, the Dlite 7, 10, 14 and Ilite 6, 8, 10 ranges. Back connections are much more suited to tiled displays as the mask 93 can be very much smaller. As shown in the drawing the connectors 99,100 extend in a direction opposite to the display direction.
It can therefore be seen that, in at least the art of electroluminescent displays, it is desirable to produce an arrangement that provides adequate heat dissipation and that is preferably also suitable for assembly of multiple arrays to generate tiled display arrangements.